1. Field of the Invention
The present invention relates to high speed, high cycle solenoid ball poppet valves, and it relates particularly to such valves having sufficiently close-tolerance durability for use as fuel injector actuators.
2. Description of the Prior Art
Some fuel injectors for internal combustion engines, either diesel or gasoline fueled, are actuated and timed by means of a solenoid ball poppet valve for each injector. For each injection cycle such valve shifts between a solenoid-actuated supply position in which the valve supplies high pressure fluid to an injector piston, and a solenoid-unactuated vent position in which the high pressure supply fluid is blocked and fluid is vented from the injector piston. Typically, such injector actuator solenoid valve will have a pair of ball poppets, one for supply and one for vent, one ball being directly engaged and actuated by the end of a solenoid plunger pin, and the other ball being actuated by a separator pin slideably mounted between the two balls with its opposite ends engageable against the respective balls.
Conventional practice in solenoid-actuated ball poppet valves has been to provide squared-off ends on the solenoid plunger pin and the separator pin. While this is satisfactory for most ball poppet valve usages, it is not satisfactory for the fuel injector use because it involves point contacting between the flat pin ends and the ball poppets, and in the fuel injector use, these point contacts involve high contact stresses which are repeated at high frequency and are applied over a very high cycle life. In the fuel injector use, fluid pressures on the ball poppets range from approximately 600 to approximately 1,500 psig, causing high point contact forces and consequent stresses. The fuel injector cycling rate is up to 120 Hertz or cycles per second, so the point contact stresses between pin ends and balls are repeated at a rate of up to 120 Hertz. For the fuel injector use, the valve must be able to withstand as many as 500 million to a billion cycles, and long before such high cycle life is achieved, such point contact stresses would result in substantial pin end deformation that would interfere with accurate repeatability of valve function during the life of the valve and would ultimately render the valve inoperative for its intended purpose because of close solenoid tolerance to obtain the necessary actuating force.
In addition to this problem of pin end distortion and consequent lack of accurate repeatability and loss of the required close tolerance over a high cycle life, the conventional flat pin ends tend to cause unpredictable eccentric engagement of the ball poppets against their respective valve seats, and this in turn causes two problems. First, the resulting irregularities in ball seating result in a lack of accurate repeatability of valve functioning, and in the fuel injector actuator usage, accurate valve function repeatability is very important. Second, such irregular, eccentric ball seating causes valve seat wear during the high cycle life to which such valves are subjected in the fuel injector usage, which will ultimately result in improper valve operation.